Enhanced in vitro biocompatibility/bioactivity of biodegradable Mg–Zn–Zr alloy by micro-arc oxidation coating contained Mg2SiO4

There is a great attraction to apply magnesium alloy as an orthopedic implant material due to its biodegradable feature and suitable mechanical properties. In order to further improve the biocompatibility of magnesium alloy, a Mg2SiO4-containing micro-arc oxidation (MAO) coating was generated on ZK60 magnesium alloy, in this study. The surface characterization by SEM, XRD and EDS showed that a rough and porous reaction layer with major composition of O, Mg and Si was formed on the surface of ZK60 alloy. The result of polarization test showed that the MAO coating significantly enhanced the corrosion resistance of biodegradable ZK60 alloy. In vitro biocompatibility/bioactivity evaluation of the MAO-coated alloy compared with the naked alloy was performed using murine bone marrow stem cells (BMSCs). The results revealed that the extract of MAO-coated alloy had no obvious cytotoxicity during the 5 days culturing, and the surface of MAO coating exhibited a better cell adhesion and affinity. Alkaline phosphatase (ALP) activity assay demonstrated that the ALP level of the BMSCs in the extract of MAO-coated alloy was much higher than that of the naked alloy, indicating that the release of Mg and Si ions from the coating was beneficial for the differentiation of BMSCs. Result of blood hemolysis test showed that the MAO coating group had a drastically decreased hemolytic ratio (1.04%) compared with the naked alloy group (28.78%) (p < 0.01), meaning a great improvement of hemocompatibility. In conclusion, the results of this study suggested that the Mg2SiO4-containing MAO coating is an effective way to improve the biocompatibility/bioactivity of magnesium alloys.